If something is aseptic it is sterile, sanitized, or otherwise clean of infectious organisms. Hospitals make every effort to keep operating rooms aseptic so that patients don’t contract infections after surgery.
The prefix “a-” almost always means that a word means the opposite of its base. The adjective aseptic, “a-” plus the root “septic,” describes anything that is not septic or is without sepsis. The origin of septic is the Greek word septikos meaning “characterized by putrefaction.” Putrefaction is the rot that happens to flesh after it dies, and when something is aseptic it is free of any rot, filth, bacteria or viruses that could cause disease or death.